Toyota's green reputation is getting a bit dirty this week. On Friday, the Union of Concerned Scientists joined the ranks of those lambasting the car company for opposing a stronger fuel-economy standard provision in the Senate energy bill.

"Toyota is working with Detroit's Big Three in a misinformation campaign to persuade Congress to drop the Senate's fuel economy proposal and replace it with a weak, loophole-ridden alternative," David Friedman, a research director for the Union of Concerned Scientists, said in a statement.

Friedman went on to say that Toyota's competitor Nissan not only supports the fuel economy provision, but also has committed to an even more aggressive target than the one laid out in the Senate provision.

The public badgering took root Tuesday when The New York Times Op-Ed Columnist Thomas L. Friedman called the top-selling, hybrid-car maker out, questioning its motives.

But Toyota hasn't stayed quiet on the matter. In a company blog, Toyota's Corporate Communications Vice President Irv Miller bit back. As to why Toyota is not giving its support? "The answer is simple: It's because there's a point at which the bar is set too high for all competitors," Miller wrote.

Instead, Toyota has steered away from the stringent fuel-economy standard provision in the Senate energy bill, for a less severe piece of legislation sitting before the House of Representatives. That must be the one David Friedman from the Union of Concerned Scientists refers to as "loophole-ridden."